Study on the Flow Characteristics of the Sweeping Jet Actuator

Abstract

The current research experimentally and computationally examines the effect of the geometric modifications on a fluidic oscillator. This fluidic actuator is a double feedback loop actuator, called Sweeping Jet Actuator (SWJ). These SWJ actuators emit a continuous but spatially oscillating jet when pressurised with a fluid thought a Coanda effect dynamics, without the requirement of any moving part. In the current thesis, unsteady flow fields generated by SWJ actuator are investigated using two-dimensional (2D), unsteady, with SST k-w and Reynolds Stress Model (RSM) simulations with Ansys v17 Fluent software over a practical range of geometric parameters. The effect of varying feedback channel height and width, internal surfaces, and scaling effect are presented. The jet frequencies of the SWJ actuator were obtained the unsteady static pressure in different locations and for different inlet mass flow rate conditions with varying the mentioned geometric parameters, using computational and experimental techniques. The modification of the height feedback channel geometry of SWJ does not affect the oscillation frequency. However, the sharpness of the first harmonic is wider for small feedback channels. The second modification performed, the feedback channel width, shows that the oscillation frequency decays for wider feedback channels making the jet oscillation well defined. The third geometric modification, internal Coanda surface, shows an increment in the frequency for a particular geometry. Finally, the scale effect shows a constant Strouhal number versus mass flow rate for all of the geometries, where the smallest geometry has the highest frequency. This research demonstrated the sharpness of the harmonic peak with the turbulence kinetic energy, which results are presented in the following chapters. Moreover, the pressure drop through the SWJ actuator has been studied and depicts that the presented geometric modifications clearly affect to pressure required to expel the oscillating jet. On the other hand, the SWJ actuator has been employed and study experimentally to minimize power consumption and the associated environmental impact in ground vehicles. The aerodynamics of ground vehicles has three-dimensional turbulent wakes are created and result in a significant separation of the flow at the back part of the car. For this reason, the SWJ actuator has been placed on the back a bluff body and tested in a wind tunnel to see the effect of the jet oscillation on the turbulent wakes. The current results show a control of the bistable wake for a certain inlet mass flow rates.

Date of Award	Jul 2019
Original language	American English